It depends on the individual school's application process. Some will hold the scores in limbo and wait for the app to come thru, others will have no idea what to do with it. It all depends on what software they are using.
Most schools will be OK with the scores if they are within a year or so of the application, but you would need to check with the individual school
Since it won't cost you anything to send the scores on the test day you might as well do it then, you won't be out any $$$ for doing it that way. If you wait (even until the day after you take the test) you will need to pay the extra fees -- personally I think that sucks, ETS should allow you to send the initial set of 3 or 4 anytime within a reasonable time period after taking the test.